Electronic timing system



Dec. 20, 1949 c. B. STADUM ET AL 2,492,015

ELECTRONIC TIMING SYSTEM Filed Jan. 27, 1947 as /.5/ 137 "IF 83 INVENTORS C /arence..5. 5 faa um and NIY/I'an) Elarye.

ATTORNEY WITNESSES:

.supply voltage 'in length .terval of another preselectednumberof half- Patented Dec. 20, 1949 UNITED STATES PATENT OFFiQiF;

ELECTRONIC TIMING SYSTEM Application January 27,1947, Serial'No. 724,622

Claims.

This invention relates .to an electronic timing 1 system, and it. has particular relation to a timing system for use with a resistance welder.

In a resistance seam welder or pulsation spot welder, as constructed in accordance with the teachings of the prior art, current is supplied from an alternat ng voltage source to the welding transformer in spaced impulses. Each impulse. is a preselected number of half-periods of the with a time in-.

periods between successive impulses. The time during which current is supplied to the welding transformer is known as the on time, period While the interval between successive impulses is known as the off time period. An overall timer is sometimestprovided to prevent further supply of a current to thewelding transformer after. a preselected number of complete operations, each of which comprises an on time and an off time period.

It is an object of ourinvention to provide a novel electronic timing system suitable for uselin controlling a resistance seam welder or pulsation spot welder.

Another object of our invention is to provide a;

new and improved timing system for a seam welder or pulsation spotwelder which is more reliable in operationand less expensive in both original and maintenance costs.

A further object of our invention is to providea new and. improved control .circuitfor use in supplying current to a load in spaced impulses with each impulse being of a predetermined length with a predetermined time interval between successive impulses.

Stillanother object of our invention isto.v pro vide a newand simplified system for timing a series of events, each of which comprises a first interval of a preselected length and a second interwith each impulse being of a predetermined length with a predetermined.time-interval between successive impulses and incorporating apparatus for preventing further supply of current after a preselected number of impulses.

In accordance with our invention, we provide a timing system for. use in supplying current to an impedance load from a voltage supply source which comprises a normally non-conductive electric control valve in series with the source and load. The valve is arranged to be conductive when a predetermined charge exists ona first capaci-.,

tor and first circuit means are provided normally tending to effectcharging of that first capacitor at a predetermined rate. Second circuit means are provided toeffect charging of a second capacitor at a predetermined rate only while the valve is conductive. When the second capacitor attains a certain charge, a discharge circuit is completed across each of the capacitors until they are substantially discharged. Consequently, the valve becomes non-conductive a predetermined time intervalafter it'first becomes conductive. Reoperation of the system is automatic until a preselected number of operations has been completed. At that time a blocking arrangement is operable to prevent-recharging of the first capacitor and thereby'to prevent further reoperation of the system.

In a resistance welding system, the voltage developed across the impedance load while the valve is conductiveimay be used with a follow-up circuit to control the firing of a pair of inversely connected main valves interposed between an alternating supply voltage source and the primary winding of the welding transformer.

The novel features that I consider characteristic of my invention are set forth with particularity with the appended claims. The invention itself, however, together with additional objects and advantages thereof, may be best understood from the following description of a specific embodiment when read in connection with the accompanying drawing, in which:

The single figure is a schematic circuit diagram of a control system embodying my invention.

As shown in the drawing, a welding transformer 3 has its primary winding 5 connected belike type, preferably a gas-filled tube such as a has its anode 31 connected to the anode 3&3 of

the second ignitron I3 through a limiting resistor 4|, and its cathode 53 connected tothe igniter 55 of the second ignitron. These valves 23 and 35 are referred to hereinafter as the first and second firing valves, respectively.

During a half-period of the supply voltage of one polarity, the anode 2'1 of the first ignitron I I is positive with respect to the cathode 51 of that ignitron. If the first firing valve 23 becomes conductive during that half-period, current flows render the latter conductive. Similarly, during a half-period of the supply voltage of opposite polarity, the anode 39 of the second ignitron I3 is positive with respect to the cathode 59 of that ignitron so that if the second firing valve 35 becomes conductive during that half-period, current flows through the igniter 55 and cathode 59 of the Second ignitron I3 to render that ignitron conductive.

Operation of the firing valves 23 and 35 is controlled by the combined effects of a peaking transformer (ii, a control transformer 53 and certain direct-current biasing voltages provided through resistors 55 and 31 in the control circuits of the firing valves extending from the control electrode 54 to the cathode 3| of the first firing valve 23 and from the control electrode 55 to the cathode 53 of the second firing valve 35. The peaking transformer is energized from the alternating voltage supply lines through an auxiliary supply transformer 68 and a phase-shifting circuit 69 and tends to render the firing valves 23 and 35 conductive alternately in successive halfperiods at a preselected instant in a half-period.

The tendency of the peaking transformer GI to cause the firing valves 23 and 35 to become conductive is normally overcome by the control transformer 53 which is energized through the auxiliary transformer 68 to provide an alternating bias voltage. However, a pair of auxiliary valves H and I3, preferably of the arc-like type, such as thyratrons, are connected in inverse relation to each other and in parallel circuit relation with the primary winding [5 of the control transformer 63. When one of these auxiliary valves l! and 13 is conductive, the bias voltage of the control transformer 63 is removed or substantially reduced so that the peaking transformer 0| is effective to render the corresponding one of the firing valves 23 and 35 conductive.

The first auxiliary valve fl is arranged to become conductive in a positive half-period only when a voltage exists across an output resistor 11 of a suitable timing circuit. By a positive halfperiod is meant a half-period in which the voltage supplied across a valve is of such polarity that the valve conducts current if a suitable voltage is applied to its control electrode.

The second auxiliary valve I3 is controlled by a follow-up arrangement I9 so that it always becomes conductive in each half-period immediately following a half-period in which the first auxiliary valve II is conductive. Thus, as long as a voltage exists across the output resistor l! in each positive half-period of the first auxiliary valve 1 I, the ignitrons l I and I3 are rendered conductive alternately in successive half-periods. When no voltage exists across the output resistor 11, the ignitrons remain non-conductive.

A more complete description of the ignitron circuits, the control circuits for the firing valves 23 and 35, the energizing circuits for the peaking transformer 5| and control transformer 53, and the follow-up arrangement, as well as the operation thereof, may be found in the copending apthrough the first firing valve 23 and the igniter I 33 and cathode 5'! of the first ignitron II to 4 plication of E. C. Hartwig, W. E. Large and C. B. Stadum, Serial No. 702,204, filed October 9, 1946.

The output resistor 11 of the timing circuit is connected in series with another resistor ill and a control valve 83 across the terminals of a sec ondary winding 85 of a supply transformer 81 energized from the supply lines. The control valve 83 is preferably of the arc-like type, such as the thyratron, and has its anode 89 connected to the right-hand terminal of the secondary winding 85 while its cathode 9| is connected through the resistors "I1 and SI to the left-hand terminal. Thus, the output resistor "I1 is energized only while the control valve 83 is conductive.

Another circuit extends from the right-hand terminal of the secondary winding 85 through two adjustable resistors 93 and 95, the anode 91 and cathode 99 of a rectifier tube IOI, an off time capacitor I03 and a conductor I05 to the left-hand terminal of the secondary winding 85. A discharge circuit is provided across the off time capacitor I03 which includes an adjustable resistor I01, an originally closed contact I09 of a relay III and another resistor H3.

The control circuit of the control valve 83 may be traced from the control electrode II5 thereof through a grid resistor IIB, an auxiliary capacitor II! to an intermediate tap II9 on a potentiometer I2I and from the lower terminal of the potentiometer I2I through the off time capacitor I03, the conductor I05 and the resistors 11 and BI to the cathode 9|.

The auxiliary capacitor I I1 is connected in circuit with a resistor I23 across another secondary winding I25 of the supply transformer 81. The arrangement results in an alternating voltage appearing across the auxiliary capacitor I H which leads the anode-to-cathode voltage of the control valve 83 by approximately The potentiometer I2I is connected in shunt across another capacitor I21 which is connected in series with another anode I29 and the cathode 99 of the rectifier tube IOI across still another secondary winding I3I of the supply transformer 81. Consequently, a unidirectional biasing voltage appears across the portion of the potentiometer I2I in the control circuit of the control valve 83 which tends to maintain the control electrode I I5 negative with respect to the cathode 9 I. The combined voltage of the potentiometer I2I and the auxiliary capacitor II! in the control circuit of the control valve 83 is normally sufficient to maintain the control valve non-conductive. However, it is apparent that if the contact I09 of the relay III is opened to break the discharge circuit across the off time capacitor I03, that capacitor is charged at a predetermined rate through the rectifier tube IOI. The polarity of the charge on the off time capacitor I03 is such that the control electrode I I5 of the control valve 83 becomes more positive. Consequently, when the charge on the off time capacitor I03 attains a predetermined value, the resultant voltage in the control circuit of the control valve 83 becomes more positive than the critical value of the valve which is necessary to render the control valve conductive in a positive half-period. Because of the pulsations provided across the auxiliary capacitor N1, the control valve 83 is rendered conductive near the beginning of each positive halfperiod so long as the charge on the off time capacitor is at least as great as is necessary to make the resultant voltage more positive than the critical value.

The operating coil I33 of the relay III is con.

"nected to be energized from the auxiliary trans of the capacitor I83 which is determined by the setting of the adjustable resistors 93 and 95 in the charging circuit. This time interval is the olr time period.

While the control valve 83 is rendered conductive in successive positive half-periods, the output resistor 11 is energized to effect firing of the ignitrons I I and I3 controlling the welding transformer. A second on time capacitor I31 is connected in parallel circuit relation with the output resistor 11 to be charged by current flowing through the control valve 83. This circuit may be traced from the cathode 9| of the control valve 83 through an adjustable resistor I39, another resistor MI, the anode I43 and cathode 455 of another rectifier tube I41, the on time capacitor I31 and the conductor I95 to the left-hand terminal of the secondary winding 85. A discharge circuit is provided across the on time capacitor I31 through a resistor I49 and another originally closed contact I5I of the relay III.

It is thus evident that so long as the relay III is energized, the on time capacitor I31 is charged only while the control valve 83 is conductive at a rate determined by the setting of the adjustable resistor I39.

An additional discharge circuit is. provided across the off time capacitor I83 which includes another normally non-conductive valve I53, preferably of the arc-like type, such as a thyratron, and a resistor I55. The control circuit of this valve I53 may be traced from the control electrode I51 through a grid resistor I59, another resistor IBI, still another resistor I63 to an intermediate terminal I6 1 on a potentiometer I69 and from the lower terminal of the potentiometer I69 through another resistor IN, the on time capacitor I31, a conductor I13 and the resistor I55 in the auxiliary discharge circuit of the off time capacitor I31 to the cathode I15 of the valve.

Originally, no voltage appears across the resistor I5I the control circuit of the valve H53 but a pulsating unidirectional voltage having the wave form of a full wave, rectified and inverted alternating voltage appears across the resistor I63 derived from another secondary winding I55 of the supply transformer 81 through rectifiers The potentiometer I69 is connected in series with the resistor III across another secondary winding I1? of the supply transformer 91 through another anode :19 and the cathode I45 of the rectifi'er tube I41. A capacitor It! is connected in shunt across theseries connected potentiometer j I69 and resistor I1I' so that a smoother directcurrent biasin voltage is impressed in the controlcircuit of the valve I53 by the potentiometer I69 and resistor Ill. The combination of the biasing voltage across th potentiometer I69 and the control circuit of the valve I53 renders that valve conductive at the beginning of each halfperiod of th alternating voltage supply. When the valve I53 is rendered conductive, it remains conductive until the off time capacitor I83 is substantially completely discharged therethrough. The discharge of the off time capacitor I03 is quite rapid and upon its discharge below the predetermined value, the control valve 83 no longer becomes conductive.

Another auxiliary discharge circuit is provided across the on time capacitor I31 through another valve I83, a resistor i 85 and the primary Winding I8: of an auxiliary transformer I89. This valve I83 also is preferably of the arc-like type, such as a thyratron, and is normally nonconduc- The control circuit of the valve I83 may be traced from its control electrode I9I through a grid resistor E93, another resistor I across which a biasing voltage is provided from a suitable source represented. by a battery I91, the resistor I 55 in the auxiliary discharge circuit of the on? time capacitor I93, the primary winding ii of the auxiliary transformer I89 and the resistor l8-5 to the cathode H9. The biasing voltage across the resistor I95 is normally sufficient to maintain the valve I83 non-conductive. However, when the auxiliary discharge circuit across the off time capacitor I93 is completed, current flows through the valve I53 and the resistor I55 to develop a voltage pulse across the resistor I55. This voltage pulse is sufficient to overcome the biasing voltage and render the valve I83 conductive to complete the discharge circuit across the on time capacitor E31. Thus when the on time capacitor 3? attains a predetermined charge, a discharge circuit is completed across each or the capacitors I93 and I31 to effect substantial discharge thereof. It is then apparent that recharging of the off time capacitor I93 is begun and the control valve 83 again becomes conductive after an off time interval.

It is to be noted that there is preferably a me chani'cal interconnection, represented by the dotted line 269, between the adjustable arms of the resistor 95 in the charging circuit of the oif time capacitor I93, and of the resistor I91 in the originally closed discharge circuit of the on time capacitor. The arrangement provides a greater resistance in the discharge circuit when the rate of charge is less. The purpose of this interconnection is to decrease the first off time period when the setting for the off time period is increased. The first olf time period occurs before any welding current is supplied and so need not be of the same length as subsequent on" time periods to effect a good weld. This first oil time period may be made shorter by increasing the resistance in the originally closed discharge circuit which increases the original charge on the off time capacitor so that the capacitor need not receive so much additional charge before the on time period begins. The interconnection between the arms of resistors 95 and I91 enables an appropriate resistance to be maintained in the discharge circuit.

A blocking arrangement is provided to halt the operation of the timing circuit after a predetermined number of on time intervals. The blocking circuit includes a blocking: valve 20!, pref.- erably of the arc-like type, such as a thyratron, having its anode 293 and cathode 295 connected in series with the primary winding 291? of an auxiliary transformer. 299- and a resistor 2H across sistor 25! to the cathode 237.

another secondary winding 2L3 of the supply transformer 83. The secondary winding 2I'5 of the auxiliary transformer 209 is connected through a rectifier 2!] across the resistor lfil in the control circuit of the valve I53 in the auxiliary discharge circuit of the oif time capacitor I03. Thus, when the blocking valve 2! is conductive in positive half-periods, a voltage appears across the resistor lEl in the control circuit of the valve !53 which is of such polarity and magnitude as to render the valve I53 conductive regardless of the condition of charge or discharge of the on time capacitor E37. Consequently, effective charging of the off time capacitor I03 is prevented so long as the valve l53 becomes conductive in each positive half-period.

The control circuit of th blocking valve 2! may be traced from the control electrode 2I8 thereof through a grid resistor 2I9, a blocking capacitor 122i, a conductor 223 to an intermediate tap 2213 on another potentiometer 225 in shunt with potentiometer H39 and from the lower terminal of potentiometer 225 through resistor Hi, the resistor 2H and primary winding 2'! to the cathode 285. The blocking valve is normally maintained non-conductive by the biasing voltage provided by potentiometer 225 and resistor I'll.

A discharge circuit is provided across the blocking capacitor 22! and includes a resistor 229 and another originally closed contact 23! of the relay Ill. The blocking capacitor 22! is also connected in a circuit extending from the left-hand terminal of another secondary winding 233 of the supply transformer 81 through the anode 235 and cathode 237 of another valve 239, a resistor 24I, an adjustable resistor 2 33, and the blocking capacitor 22I and conductor 223 to the righthand terminal of the secondary winding 233. Therefore, while relay l i i is energized, the blocking capacitor 22l is charged at a predetermined rate, determined by the setting of the adjustable resistor 2 13, whenever the valve 239 is conductive.

The control circuit of the valve 239 may be traced from its control electrode 245 through a grid resistor 25?, the secondary winding 249 of the auxiliary transformer I89, and another re- A capacitor 253 and. resistor 255 are connected in series across the secondary winding 249. A biasing voltage appears across the resistor 25l which is normally sufficient to maintain the valve 239 non-conductive. However, an additional voltage pulse is introduced into the control circuit of the valve 239 upon a discharge of the on time capacitor 533 through the primary winding I87 of the auxiliary transformer 1133. Since the voltage pulse is of extremel short duration and occurs at the very beginning of a positive half-period of the valve 233, the capacitor 253 is provided to insure the valve becoming conductive for one half-period to supply an increment of charge to the blocking capacitor 222i. While valve 239 does not become conductive until after valve I83 becomes conductive, and valve 583 follows valve I53, the action is so fast that valve 239 becomes conductive very near the beginning of a half-period. Consequently, the blocking capacitor 22l is charged in steps, receiving a predetermined increment of charge each time the on time capacitor IE3! is discharged. After a preselected number of discharging operations of the on time capacitor, as determined by the setting of the ad- Justable resistor 243, the blocking capacitor charge becomes suflicient to render the blocking valve 20I conductive and prevent further operation of the timing circuit.

The operation of the system may be initiated by closure of the push-button switch I35 to energize the relay III. The relay contacts I09, I5l and EM open the discharge circuits across the off time, on time and blocking capacitors I03, I31 and 22I. As a result, charging of the off time capacitor I03 at a predetermined rate is initiated. After a predetermined time interval which may be relatively short because of the setting of the resistor I01, the on" time capacitor I03 is sumciently charged to cause the control valve 83 to become conductive in positive half-periods of its supply voltage.

While the control valve 83 is conductive, a voltage appears across the output resistor TI to cause the first auxiliary valve II to become conductive. The connections are such that the positive half-periods of the first auxiliary valve II coincides with the positive half-periods of the control valve 83, the firing valve 23 and the corresponding ignitron I I.

When the first auxiliary valve II is conductive, it effectively removes the biasing voltage of the control transformer 63 permitting the firing valve 23 to render the ignitron I! conductive at the instant of the half-period determined by the peaking transformer 6|. In the next succeeding half-period, the second auxiliar valve I3 becomes conductive because of the follow-up arrangement, causing the other ignitron I3 to be rendered conductive. It is evident that when the control valve 83 becomes conductive in each positive half-period, the ignitrons II and I3 become conductive alternately in successive halfperiods to supply current through the welding transformer 3.

While'the control valve 83 is conductive, the on time capacitor I3? is charged at a predetermined rate. After another predetermined time interval, the on time capacitor I3! is sufficiently charged to render the valve I53 conductive to complete the auxiliary discharge circuit across the off time capacitor I03. The discharge of the off time capacitor I3 acts through the resistor I55 to render the other valve I83 conductive to complete the auxiliary discharge circuit across the on time capacitor I37. The discharge of the on time capacitor l3! through the auxiliary transformer I89 causes the valve 239 to become conductive for a single positive half-period to supply an increment of charge to the blocking capacitor 22 I. Unless the adjustable resistor 243 in the charging circuit of the blocking capacitor is set for but a single cycle of operation, the first increment of charge on the blocking capacitor 22I is insufficient to render the blocking valve 2M conductive.

When the off time capacitor I03 is discharged below the predetermined value, the control valve 83 no longer becomes conductive in a positive half-period. As the off time capacitor I03 is substantially discharged, the valve I53 in its auxiliary discharge circuit again becomes non-c0n ductive and recharging of the off time capacitor is again initiated, the off time period then being the full length inasmuch as the discharge circuit through resistor ll was not used. The operation is then repeated so that after a predetermined off time interval the control valve 83 becomes conductive and remains conductive for a predetermined on time interval.

After a preselected number of complete operations, as determined by the setting of the adjustable resistor 243 in the charging circuit of the blocking capacitor 22I, the charge on the blocking capacitor 22I becomes sufficient to render the blocking valve 2M conductive. A voltage pulse is then impressed in the control circuit of the valve I53 in the discharge circuit oi the off time capacitor I03, which pulse is sufiicient to render the valve conductive in each half-period in which the capacitor tends to be charged. Thus, further operation of the timing circuit is prevented. A new series may be obtained by releasing the pushbutton switch I35 to reset the system and then reclosing it.

While the system illustrated assumes manual operation of the push-button switch I35 and that it be held closed throughout the weld, it will be apparent that the switch may be operated automatically as, for example, by sequencing circuits, or other suitable means of operating the relay I I I may be employed.

It is to be noted that the usual by-pass capacitors have been shown between the control electrode and cathode of each thyratron. The thyratrons have been illustrated as of the indirectly heated type but the usual connections for supplying current through the filaments have been omitted to avoid confusion in the drawing.

While We have shown and described a specific embodiment of our invention, we are aware that many modifications thereof might be made Without departing from the spirit of the invention. It, therefore, is not our intention to limit our invention to that specific embodiment.

We claim as our invention:

1. A timing system for use in supplying current through a load from a voltage supply, comprising an electric valve in series With said source and load for controlling the flow of current through the load, a pair of capacitors, a first circuit normally tending to effect charging of one of said capacitors at a predetermined rate, a control circuit responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, a second circuit effective only while the valve is conductive to cause charging of the other capacitor at a predetermined rate, and means operable in response to a predetermined charge on said other capacitor to efiect temporary completion of a discharge circuit across each of the capacitors until they are substantially discharged.

2. A timing system for use in supplying current through a load from a voltage supply source, comprising a normally non-conductive electric valve in series with said source and load for controlling the fiow of current through the load, a pair of capacitors, a starting device, first circuit means for charging one of said capacitors at a predetermined rate following operation of said starting device, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means efiective only While the valve is conductive to cause charging of the other capacitor at a predetermined rate, and means operable in response to a. predetermined charge on said other capacitor to eifect temporary completion of a discharge circult across said one capacitor.

3. A timing system for use in supplying current through a load from a voltage supply source, comprising an electric valve in series With said source and load for controlling the flow of current through the load, a pair of capacitors, a first circuit normally tending to cheat charging of one of said capacitors at a predetermined rate, a control circuit responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means effective only While the valve is conductive to cause charging of the other capacitor at a predetermined rate, means operable in response to a predetermined charge on said other capacitor to effect temporary completion of a discharge circuit across said one capacitor until it is substantially discharged, and means operable after said predetermined charge is attained on said other capacitor to elTect temporary completion of a discharge circuit across said other capacitor until it is substantially discharged.

4. A timing system for use in supplying current through a load from a voltage supply source, comprising an electric valve in series with said source and load for controlling the flow of current through the load, a pair of capacitors, first circuit normally tending to efiect charging of one of said capacitors at a predetermined rate, a control circuit responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit effective only while the valve is conductive to cause charging of the other capacitor at a predetermined rate, means operable in response to a predetermined charge on said other capacitor to effect temporary completion of a first discharge circuit across said one capacitor until it is substantially discharged, and means operable in response to current through said first discharge circuit to effect temporary completion of a second discharge circuit across said other capacitor until it is substantially discharged.

5. A timing system for use in supplying current through a load from a voltage supply source, comprising a normally non-conductive electric valve in series with said source and load, a pair of capacitors, first circuit means connecting one of said capacitors in parallel circuit relation with the series connected valve and load to effect charging of said one capacitor at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means connecting the other capacitor in parallel circuit relation with the load and in series with the valve to be charged at a predetermined rate only While the valve is conductive, and means operable in response to a predetermined charge on said other capacitor to effect temporary completion of a discharge circuit across each of the capacitors until they are substantially discharged.

6. A timing system for use in supplying cur rent through a load from an alternating voltage supply source, comprising a normally non-conductive electric valve in series with said source and load, a pair of capacitors, first circuit means including a rectifier connecting one of said capacitors in parallel circuit relation with the series connected valve and load to effect charging of said one capacitor at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive in positive half-periods of said supply voltage, second circuit means including a rectifier connecting the other capacitor in parallel circuit relation with the load and in series with the valve to be charged at a predetermined rate while the valve is conductive, and means operable in response to a predetermined charge on said other capacitor to eiiect completion of a discharge circuit across each of the capacitors until they are substantially discharged.

l. A timing system for use in supplying current through a load from a voltage supply source,

- comprising a normally non-conductive control valve in series with said source and load, a pair of capacitors, first circuit means normally tending to effect charging of one of said capacitors at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the control valve to be conductive, second circuit means efiective only while the control valve is conductive to cause charging of the other capacitor at a predetermined rate, a first discharge circuit connected across said one capacitor and including a first normally non-conductive auxiliary valve, a second discharge circuit connected across said other capacitor and including a second normally non-conductive auxiliary valve, and means for causing said auxiliary valves upon said other capacitor attaining a predetermined charge, to become conductive temporarily until said capacitors are substantially discharged.

8. A timing system for use in supplying current through a load from a voltage supply source, comprising a normally non-conductive control valve in series with said source and load, a pair of capacitors, first circuit means normally tending to effect charging of one of said capacitors at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the control valve to be conductive, second circuit means efiective only while the control valve is conductive to cause charging of the other capacitor at a predetermined rate, a first discharge circuit connected across said one capacitor and including a first normally non-conductive auxiliary valve, means responsive to a predetermined charge on said other capacitor for causing said first auxiliary valve to be conductive temporarily until said one capacitor is substantially discharged, a second discharge circuit connected across said other capacitor and including a second normally non-conductive auxiliary valve, and means operable in response to a discharge of said one capacitor to cause the second auxiliary valve to be conductive temporarily until said other capacitor is substantially discharged.

9. A timing system for use in supplying current through a load from a voltage supply source, comprising a normally non-conductive electric valve in series with said source and load, a pair of capacitors, first circuit means connecting one of ductive electric valve in series with said source and load, a pair of capacitors, first circuit means including a rectifier connecting one of said capacitors in parallel circuit relation with the series connected valve and load to effect charging of said one capacitor at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive in positive half-periods of said supply voltage, second circuit means including a rectifier connecting the other capacitor in parallel circuit relation with the load and in series with the valve to be charged at a predetermined rate while the valve is conductive, a first discharge circuit connected across said one capacitor and including a first normally non-conductive auxiliary valve, a second discharge circuit connected across said other capacitor and including a second normally non-conductive auxiliary valve, and control means for causing said auxiliary valves upon said other capacitor attaining a predetermined charge, to become conductive temporarily until said capacitors are substantially discharged.

11. A timing system for use in supplying current through a load from an alternating voltage supply source, comprising a normally non-conductive electric valve in series with said source and load, a pair of capacitors, first circuit means including a rectifier connecting one of said capacitors in parallel circuit relation with the series connected valve and load to effect charging of said. one capacitor at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive in positive half-periods of said supply voltage, second circuit means including a rectifier connecting the other capacitor in parallel circuit relation with the load and in series with the valve to be charged at a predetermined rate while the valve is conductive, a first discharge circuit connected across said one capacitor and. including a first normally non-conductive auxiliary valve, means responsive to a predetermined charge on said other capacitor for causing said first auxiliary valve to be conductive temporarily until said one capacitor is substantially discharged, a second discharge circuit connected series connected valve and load to efiect charging of said one capacitor at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means connecting the other capacitor in parallel circuit relation with the load and in series with the valve to be charged at a predetermined rate only while the valve is conductive, a first discharge circuit connected across said one capacitor and including a first normally non conductive auxiliary valve, a second discharge circuit connected across said other capacitor and including a second normally non-conductive auxiliary valve, and control means for causing said auxiliary valves upon said other capacitor attaining a predetermined charge, to become conductive temporarily until said capacitors are substantially discharged.

10. A timing system for use in supplying current through a load from analternating voltage supply source, comprising a normally non-conacross said other capacitor and including a second normally non-conductive auxiliary valve, and means operable in response to a discharge of said one capacitor to cause the second auxiliary valve to be conductive temporarily until said other capacitor is substantially discharged.

12. A timing system for use in supplying current through a load from a voltage supply source, comprising a normally non-conductive electric valve in series with said source and load for controlling the flow of current through the load, a pair of capacitors, first circuit means normally tending to effect charging of one of said capacitors at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means effective only while the valve is conductive to cause charging of the other capacitor at a predetermined rate, means operable in response to a predetermined charge on said other capacitor to effect completion of a discharge circuit across each of the capacitors until they are substantially discharged, and means operable after said capacitors have been discharged a preselected number of times to prevent recharging of said one capacitor.

13. A timing system for use in supplying current through a load from a voltage supply source,

comprising a normally non-conductive electric valve in series with said source and load for controlling the flow of current through the load, a pair of capacitors, first circuit means. normally tending to effect charging of one of said capacitors at a predetermined rate, control means responsive to a predetermined charge on said. one capacitor to cause the valve to be conductive, second circuit means effective only While the valve is conductive to cause charging of the other capacitor at a predetermined rate, means operable in response to a predetermined charge on said other capacitor to effect completion of a discharge circuit across each of the capacitors until they are substantially discharged, and means responsive to each discharge of said other capacitor and operable after a preselected number of such discharges to prevent recharging of said one capacitor.

14. A timing system for use in supporting current through a load from a voltage supply source, comprising a normally non-conductive electric Valve in series with said source and load for controlling the flow of current through the load, a

pair of capacitors, first circuit means normally tending to effect charging of one of said capacitors at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means effective only while the valve is conductive to cause charging of the other capacitor at a predetermined rate, means operable in response to a predetermined charge on said other capacitor to efifect completion of a discharge circuit across each of the capacitors until they are substantially discharged, a third capacitor, means responsive to each discharge of said pair of capacitors for providing an increment of charge on the third capacitor, and means responsive to a predetermined charge on the third capacitor for preventing recharging of said one capacitor.

15. A timing system for use in supplying current through a load from a voltage supply source, comprising a normally non-conductive electric valve in series With said source and load for controlling the flow of current through the load, a pair of capacitors, first circuit means normally tending to eiTect charging of one of said capacitors at a predetermined rate, control means responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means effective only while the valve is conductive to cause charging of the other capacitor at a predetermined rate, a, first discharge circuit connected across said one capacitor and including a first normally non-conductive auxiliary valve, a second discharge circuit connected across the other capacitor and including a second normally non-conductive auxiliary valve, means for causing said auxiliary valves upon said other capacitor attaining a predetermined charge, to become conductive temporarily until said pair of capacitors are substantially discharged, a third capacitor, means responsive to each discharge of said pair of capacitors for providing an increment of charge on the third capacitor, and means responsive to a predetermined charge on the third capacitor for causing said first auxiliary valve to be conductive regardless of the charge on said other capacitor to prevent recharging of said one capacitor.

16. A timing system comprising a capacitor, means adapted to function as a source of voltage, first circuit means connecting said source all with said capacitor and tending to charge the capacitor at a predetermined rate, means respon; sive to a predetermined charge on the capacitor for temporarily completing a discharge circuit thereacross until the capacitor is discharged, an originally closed shunt circuit across said capacitor, and a starting device for opening said shunt circuit, said shunt circuit including impedance means aifording an original charge on the capacitor to cause the time required for the capacitor to reach said predetermined charge immediately following operation of said starting device to be substantially less than the time required following discharge of the capacitor through the discharge circuit.

17. Apparatus according to claim 16 in which said first circuit means includes an adjustable impedance having an adjusting member for setting the rate of charge of the capacitor and said impedance means is adjustabe and has an adjusting arm, and which includes means interconnecting said arm and member for simultaneous and corresponding adjustment thereof.

18. A timing system for use in supplying current through a load from a voltage supply, comprising an electric valve in series with said source and load for controlling the flow of current through the load, a pair of capacitors, a first circuit normally tending to effect charging of one of said capacitors at a predetermined rate, a control circuit responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, second circuit means effective to cause charging of the other capacitor at a predetermined rate, and means operable in response to a predetermined charge on said other capacitor to efiect temporary completion of a discharge circuit across each of the capacitors until they are substantially discharged.

19. A timing system for use in supplying current through a load from a voltage supply, comprising an electric valve in series with said source and load for controlling the flow of current through the load, a pair of capacitors, a first circuit normally tending to eifect charging of one of said capacitors at a predetermined rate, a control circuit responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, a second circuit effective to cause charging of the other capacitor at a predetermined rate, means operable in response to a predetermined charge on said other capacitor to efliect temporary completion of a discharge circuit across said one capacitor until it is substantially discharged, and means operable after said predetermined charge is attained on said other capacitor to efiect temporary completion of a discharge circuit across said other capacitor until it is substantially discharged.

20. A timing system for use in supplying current through a load from a voltage supply, comprising an electric valve in series with said source and load for controlling the flow of current through the load, a pair of capacitors, a first cir-.

cuit normally tending to eiiect charging of one of said capacitors at a predetermined rate, a control circuit responsive to a predetermined charge on said one capacitor to cause the valve to be conductive, a second circuit effective to cause charg ing of the other capacitor at a predetermined rate, means operable in response to a predetermined charge on said other capacitor to effect temporary completion of a first discharge circuit across said one capacitor until it is substantially discharged, and means operable in response to 15 16 current through said first discharge circuit to REFERENCES CITED effect temporary completion of a second discharge circuit across said other capacitor until it is subg z ifig g i are of record m the stantially discharged. p

5 UNITED STATES PATENTS g i 53 Number Name Date 2,006,737 Gessford July 2, 1935 2,340,077 Pearson Jan. 25; 1944 

